1. Field of the Invention
The present disclosure relates generally to crystalline material growth systems, and, more particularly, to an advanced crucible support and thermal distribution management.
2. Description of the Related Art
Crystal growth apparatuses or furnaces, such as directional solidification systems (DSS) and heat exchanger method (HEM) furnaces, involve the melting and controlled resolidification of a feedstock material, such as alumina or silicon, in a crucible to produce an ingot or boule. Production of a solidified product from molten feedstock occurs in several identifiable steps over many hours. For example, to produce a silicon ingot by the DSS method, solid silicon feedstock is provided in a crucible, often contained within a graphite crucible box, and placed into the hot zone of a DSS furnace. Alternatively, to produce, for example, a sapphire boule by the HEM method, solid feedstock, such as alumina, is provided in a crucible containing a monocrystalline seed (which comprises the same material as the feedstock but with a single crystal orientation throughout) placed into the hot zone of a solidification furnace. A heat exchanger, such as a helium-cooled heat exchanger, is positioned in thermal communication with the crucible bottom and with the monocrystalline seed. The feedstock is heated to form a liquid feedstock melt, without substantially melting the monocrystalline seed, and the furnace temperature, which is well above the seed melting temperature, is maintained for several hours to ensure proper melting. Once melted, heat is then removed from the melted feedstock by applying a temperature gradient in the hot zone, in order to directionally solidify the melt from the substantially unmelted seed to form the boule. By controlling how the melt solidifies, a crystalline material having a crystal orientation corresponding to that of the monocrystalline seed can be achieved, and having greater purity than the starting feedstock material, can be achieved.
For stability, crucibles are placed into a furnace atop a support structure that generally matches the shape of the crucible's base. Typically, these supports are a solid material, and may generally take the shape of a solid ring, in which the crucible sits. The current crucible support design, however, limits the “view factor” for radiated heat generated from a furnace's heating element from reaching the bottom of the crucible. Because of this fact, the temperature gradient at the base of the crucible is not ideal.
Additionally, the current method of using the crucible itself as a means for establishing a physical interface for a given crucible manipulating device is presenting challenges and safety concerns as the physical size and mass of crucible and charge size increases. In the crystal growth process a ring is used for supporting of the crucible within the hot zone. The ring is currently manually loaded into the furnace as its own discrete loading step, and then several steps follow before a crucible is fully charged and considered ready for the crystal growth process, thus causing issues for any automation requirements for the crucible loading process.